Help with rendering shadows properly
From your question, I think you have one large plane pointing straight down as your light. If that is the case there in lies your problem. 

Move your light off axis. If you want your shadow to be in the same place as the shaded preview, then move it along the -X axis and towards the camera. Next rotate the light towards your ground object. Now, if the light is a a low enough angle, each hump will cast a shadow. (your text will also, but that is a different issue)